The present invention pertains to a monitoring device and particularly to such a device which will significantly improve on the reliability afforded in an electronic or electromechanical system, especially with respect to a power supply for such a system.
Many attempts have been made in the past to implement the achievement of reliability in the functioning of electrical components and particularly so where such components are concerned with providing reliable power supplies to an electronic system. The desired reliability is especially difficult to achieve in the situation where the failures that may be encountered differ substantially in nature and where failures in one of the units will affect the functioning of the other unit serving as a redundant or backup means.
Although the principle of the present invention will be disclosed in a detailed embodiment featuring the application to a power supply, it will be evident that the principle is perfectly general and can be applied to a variety of electrical components whose operation must be extremely reliable and therefore ordinarily calling for a conventional redundancy scheme.
In connection with the need to furnish a reliable power supply unit, it will be recognized that a variety of failure modes can exist and these are: loss of regulation which may take several forms; that is, the output of the supply may be too high in voltage, thus failing to meet established criteria, or the output of the supply may be too low in voltage and similarly fail. Another problem which may be presented is that the AC content may not be satisfactory; that is to say, either ripple or transient noise energy levels may become too high. Yet another possible failure is that no output voltage will be realized from a power supply unit, either for the reason that the output of the supply has become shorted, often with the consequence that the other or redundant power supply has its voltage pulled down; or, it may turn out that the output of a power supply has become open.
Accordingly, it is a primary object of the present invention to detect any one of the aforesaid failure modes in a given power supply and to connect an auxiliary power supply in its place.
However, based on the above described failure modes it is clear that if redundant power supplies are needed in order to meet a specific reliability goal, a selection device with good isolation between the supplies is necessary in order to preclude a failure in one supply causing a secondary failure in the other supply. In addition to this, and most importantly, the selection device must be capable of detecting even the aforenoted subtle failures in either of the supplies, that is to say, the aforenoted loss of regulation or the AC content being not within the specified limits.
Accordingly, it is a further primary object of the present invention to provide a selection device with the requisite isolation as aforenoted, but to achieve greater reliability than is simply attainable by a conventional redundancy scheme or system.
In accordance with the stated primary objects, the present invention provides a selection device so arranged that, for example in the particular case of power supplies, the selection device (or power supply monitor) must choose one and only one of the power supplies to supply energy to the system regardless of internal failure within the selection device itself. As will be made especially clear hereinafter, a much improved total reliability results because there is an additional possibility for success in furnishing power to the system.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawing, wherein like parts have been given like numbers.